Standards and Certified Reference Materials

An overview of the uranium and plutonium certified reference materials that are used for safeguards and fissile material control for bulk and particle analysis was presented at a conference organized by the European Joint Research Centre (JRC) (Jakopic et al. 2012). There are three main types of CRMs single isotope standards for isotope dilution measur ents CRMs for isotope ratio calibration and mass discrimination correction and reference materials for age dating. As far as uranium is concerned, there are (almost pure) mono-isotopic standards and 

The 238fj/235u jatio in standard reference materials for natural uranium has been meticulously scrutinized and revised by very precise measurements (Brennecka et al. 2010 Richter et al. 2010 Hiess et al. 2012). The NBS SRM 960 (NBL CRM 112a) served as the consensus value for of 137.88 but interlaboratory measurements with an accurate double-spike gave a slightly different average 

Interlaboratory exercises focusing on nuclear forensics have been initiated by the Joint Research Centre (JRC) of the European Community. The two most recent exercises were called NUSIMEP-6 (Aregbe et al. 2008) and NUSIMEP-7 (Truyens et al. 2013) (NUSIMEP—Nuclear Signatures Inter-laboratory Measurement Evaluation Programme). In these exercises, identical samples were sent to the participating laboratories and the predefined analytes (content and isotopic ratios) were measured and reported to the coordinators, who then compiled the results, compared them with the target value, and produced a report. The remainder of the samples that were not consumed in the measurements can subsequently serve as standards for future measurements. One other benefit of these intercomparisons is that the accuracy and effectiveness of the different analytical procedures and the instrumentation can be assessed. In addition, corrective measures can be implemented in order to improve the performance. Finally, the cooperation between the scientists and the laboratories can lead to the development of standard procedures and recommended methods. This is essential for nuclear forensics where the implications of the analytical results, as mentioned earlier, may evoke political and even military actions in some cases. 

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List all of the reagents, materials, blanks, QC samples, standards and Certified Reference Materials required for the analytical process, numbered for later reference. List the following ... 

Sample numbers have been randomised to minimise regional bias, help separate false from true anomalies and obtain meaningful estimates of the variance of duplicates. Field duplicates, analytical duplicates, in-house standards and certified reference materials are introduced at regular intervals in the analytical streams. 

Denise LeBlanc is the Group Leader for the Marine Sciences Group and the Manager of the Certified Reference Materials Program at the Institute for Marine Biosciences (IMB) of the National Research Council of Canada. The Certified Reference Materials Program manufactures instrument calibration standards and certified reference materials for shellfish toxins, PCBs, PACs, and trace elements in marine sediments, in biological tissues, and in seawater. Her experience resides in the manufacture and long-term production of reference materials. 

Wong, C.S. Hoekstra, P.E Karlsson, H. Backus, S.M. Mabury, S.A. Muir, D.C.G., Enantiomer fractions of chiral organochlorine pesticides and polychlorinated biphenyls in Standard and Certified Reference Materials Chemosphere 2002, 49, 1339-1347. 

The HPLC method most widely used has been a reversed phase chromatography, with diode array detection enabling the detection of all microcystins bases in their UV spectra (Lawton 1994). This method offers a good separation of microcystins under the gradient elution conditions nevertheless, the lack of standards and certified reference materials makes necessary that the quantitation of these toxins had to be carried out based on purified MC-LR to give MC-LR equivalence. 

Quality control (QC) refers to the operational techniques and activities that are used to fulfill requirements for quality. Internal quality control comprises the routine practical procedures that enable the analytical chemist to make a decision on whether to accept a result or a group of results as fit for purpose, or reject them and repeat the analysis. Tools for quality control include the use of reference standards and certified reference materials, the use of positive (spiked or incurred) and negative control samples and control charts, replicate analyses, and proficiency tests. Quality control in the laboratory is discussed in more detail in Section 10.5 of this chapter. 

Owing to the general lack of standards and certified reference materials of elemental species in specific matrices, application of species-unspecific quantification strategies employing... 

Chemical and Physical Standards, Calibrants, Certified Reference Materials and Reagents... 

The lack of standardization during method verification is a long-standing problem in vitamin analyses. This makes it difficult, if not impossible, to assess the validity of individual methods and to compare different assays without extensive bench work. Although standard or certified reference materials are available for the minerals in foods, development of similar materials for the vitamins is being hampered by the lability of the vitamins as well as by inconsistent results from the various analyses for the same vitamin or, in certain cases, the interlaboratory variability for the same method. 

For both consistency over each day, and to check day-to-day reproducibility, it is very useful to analyse at regular intervals either synthetic standard solutions, prepared in an appropriate matrix, or, better still, standard or certified reference materials, which contain precisely known amounts of the elements or species of interest. Routine long-term time-plots of the results of such regularly repeated analyses are very useful in showing up errors arising as a consequence of hitherto unrealized procedural changes. 

Numerous standard or certified reference materials exist for verifying the reliability of new or modified methods, especially for total mercury standard reference materials for individual organomercury species can be more difficult to obtain. The existing methods for determining mercury in biological and environmental matrices are described more fully in the following sections. 

Alvarez, A. (1984) Standard solutions and certified reference materials. Ch 50. In S. Williams (ed.), Official Methods of Analysis of the Association of Official Analytical Chemists, 14th edn. (AOAC, Washington, USA.) pp. 1002-1004. 

Perhaps the most pressing issue that needs urgent attention is that of quality assurance. To date, only two inter-laboratory exercises have been conducted the results from both smdies demonstrated that quantitative measurements can be quite varied. Consensus on the choice of a working standard solution, method of quantitation, and certified reference materials will go a long way to ensure that interlaboratory measurements are more comparable. 

There are two schemes in practice to verify and validate a laser diffraction instrument and its measmement. One is to use either reference materials (national standard or certified reference materials or secondary reference materials traceable to the national reference materials) or the instrument manufacturer s controls [20]. The average of the median size value (d5o)from at least three independent measinements should agree with the certified value of... 

NAA is a quantitative method. Quantification can be performed by comparison to standards or by computation from basic principles (parametric analysis). A certified reference material specifically for trace impurities in silicon is not currently available. Since neutron and y rays are penetrating radiations (free from absorption problems, such as those found in X-ray fluorescence), matrix matching between the sample and the comparator standard is not critical. Biological trace impurities standards (e.g., the National Institute of Standards and Technology Standard Rference Material, SRM 1572 Citrus Leaves) can be used as reference materials. For the parametric analysis many instrumental fiictors, such as the neutron flux density and the efficiency of the detector, must be well known. The activation equation can be used to determine concentrations ... 

ISO Guide 32 (1997) Calibration in analytical chemistry and use of certified reference materials. International Organization for Standardization, Geneva. 

Wise SA, Schantz MM, Poster DL, Lopez de Alda MJ, and Sander LC (2000) Standard reference materials for the determination of trace organic constituents in environmental samples. In Barcelo D, ed. Sample Handling and Trace Analysis of Pollutants Techniques, Applications and Quality Assurance, pp 649-687. Elsevier Science Publishers, Amsterdam, The Netherlands. Yoshinaga Y, Morita M, and Okamoto K (1997) New human hair certified reference material for methylmercury and trace elements. Fresenius J Anal Chem 357 279-283. 

When the American Type Culture Collection (ATCC) was founded in 1925, one of its chief roles was to be a source of standards. In this context we mean standard organisms, rather than standard materials or chemicals known as Reference Materials or Certified Reference Materials and issued in the USA by the National Bureau of Standards (NBS). The National Bureau of Standards evolved into NIST and the abbreviation SRM became a trade mark of NIST. 

Conventional XRF analysis uses calibration by regression, which is quite feasible for known matrices. Both single and multi-element standards are in use, prepared for example by vacuum evaporation of elements or compounds on a thin Mylar film. Comparing the X-ray intensities of the sample with those of a standard, allows quantitative analysis. Depending on the degree of similarity between sample and standard, a small or large correction for matrix effects is required. Calibration standards and samples must be carefully prepared standards must be checked frequently because of polymer degradation from continued exposure to X-rays. For trace-element determination, a standard very close in composition to the sample is required. This may be a certified reference material or a sample analysed by a primary technique (e.g. NAA). Standard reference material for rubber samples is not commercially available. Use can also be made of an internal standard,... 

In analytical practice, they are best recognized by the determination of xtest as a function of the true value xtrue, and thus, by analysis of certified reference materials (CRMs). If such standards are not available the use of an independent analytical method or a balancing study may provide information on systematic errors (Doerffel et al. [1994] Kaiser [1971]). In simple cases, it may be possible, to estimate the parameters a, / , and y, in Eq. (4.5) by eliminating the unknown true value through appropriate variation of the weight of the test portions or standard additions to the test sample. But in the framework of quality assurance, the use of reference materials is indispensable for validation of analytical methods. 

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